The answer to this question could be found in the mind-wandering literature (see this for a review). Figure 1 in the paper really nicely depicts the possible situations possible when looking at task engagement and self-generated thought. I'll summarize them here:
- You are engaged in the task, i.e. attention is focused outwards, and the stimuli you perceive are task-related. You are focused.
- You are generating thoughts about the task you are working on, i.e. attention is focused internally, but regarding the task. This is not a harmful state, since contemplating about something relevant may be very useful.
- You are engaged in the task, but a non-relevant stimulus is perceived (e.g. phone ringing, seeing your dirty dishes on the kitchen counter). You get distracted.
- You are generating thoughts about something completely irrelevant (e.g. your upcoming holiday. This is the most harmful state, and will only stop until you realize your mind is wandering. (I will not go into the meta-cognitive processes of this. For that, see the referenced paper).
There are thus two reasons why you fail to focus on the task at hand. (1) there are external stimuli that distract you, or (2) you distract yourself.
Task Interruptions and Multi-tasking
When the problem is that too many distracting stimuli are present, we should look at the multitasking literature. Salvucci and Bogunovic (2010) for instance, showed that workload determines how easily a distracting task/stimuli may grab your attention. The lower workload is, the more "opportunities" there are to switch to the other task. With more opportunities I mean that you use little cognitive resources on the primary task, which allows a secondary task to be attended at. This is also shown by Katidioti and Taatgen (2014) by showing that people tend to switch tasks when the time to load a webpage is rather long (3000 ms in the paper). During this period of time, a person has to wait before he can continue his task, therefore decreasing workload at the time. On the other hand, when workload is high and you are focused on the task, less opportunities exist for switching tasks. This may also be explained by "attentional narrowing", i.e. having a higher focus on one task/stimulus and, therefore, being unable to actually perceive distracting stimuli.
However, when you do get interrupted during a high-workload period, the costs of task-switching is a lot higher. It takes considerable more time to "reset" your goals and, sometimes (when you had to remember a particular fact e.g.), you must again search for that information (Salvucci & Bogunovic, 2010). This may greatly affect productivity, even more so if you consider people are interrupted every six minutes (Reference in Katidioti et al., 2010).
Self-generated Thought (SGT)
Being distracted by SGTs is also greatly affected by workload, as described in the review (as are all other statements). Again, if workload is low, there are more opportunities to "reset" your goals, i.e. to focus attention internally. On the other hand, if workload is high, you are less likely to create SGT. This effect is especially easy to see during vigilance tasks (such as studying or monitoring).
Getting distracted by yourself, i.e. focusing on SGT, is not always a bad thing though, so do not immediately try to diagnose ADHD or something. It has been shown that people that create more SGT are more creative than people who are in general more focused. Moreover, as stated earlier, SGT may be about task-relevant issues.
There are thus two reasons why one may get distracted when studying alone. There are external stimuli that grab your attentions or you just have difficulties with vigilance tasks and you distract yourself. Let me give you some tips that may help focusing your attention.
- Clean up your house before you start studying. If there is nothing to do around you, you won't have a reason to get distracted by another task. You could also try to study in a library. You definitely won't start vacuuming over there.
- Study with a fellow student. The "social pressure" (this is how I experience it) prevents me from doing other things, because I know it will also distract the other. Another benefit is that you can ask each other thing you do not understand. The downside of studying together is that the other may in fact be the distractor.
- Staying vigilant is difficult for a longer period of time. Switch between studying and walking for instance may help focusing your attention for the briefer periods of time.
- Make the material more interactive. Reading a book requires vigilance and is a really passive way of studying. Make flash cards, write a summary, create a game; anything that may help you study in a more interactive way is good.
I really hope this will help.